Punch press with safety door

ABSTRACT

The punch is surrounded by a tubular housing carrying a stripper plate and having a hinged door which is latched closed unless the punch is retracted to a tool change position. In addition, means sense the position of the door and prevent automatic cycling of the punch if the door is not closed. To adjust the stripper plate vertically, provision is made of compactly nested threaded rings and, to orient the punch angularly, provision is made of an adjusting mechanism which acts on a rod projecting from the upper end of a hydraulic cylinder and connected to a downwardly projecting ram for reciprocating the punch.

United States Patent [191 Scott et a1.

[ PUNCH PRESS WITH SAFETY DOOR [75] Inventors: William B. Scott,Steward; Roger V. Sawvell, New Milford, both of 111.

[73] Assignee: W. A. Whitney Corp., Rockford, Ill. [22] Filed: July 24,1972 [21] App]. No.: 274,391

[52] US. Cl 83/545, 83/571, 83/D1G. 1, 100/53, 192/134, 192/135 [51]Int. Cl 826d 7/24 [58] Field of Search 83/58, 68, 544, 545, 571, 83/572,DIG. 1, 573; 100/53; 192/134, 135

[56] References Cited UNITED STATES PATENTS 3,646,883 3/1972 Provi100/53 2,916,985 12/1959 Beach 100/53 3,576,162 4/1971 McBrady 100/53[11] 3,805,658 Apr. 23, 1974 3,688,686 9/1972 Ligh 100/53 X PrimaryExaminer-Frank T. Yost Attorney, Agent,.0r Firm-Wolfe, Hubbard, Leydig,Voit & Osann, Ltd.

[5 7] ABSTRACT I The punch is surroundedby a tubular housing carrying astripper plate and having a hinged door which is latched closed unlessthe punch is retracted to a tool change position. In addition, meanssense the position of the door and prevent automatic cycling of thepunch if the door is not closed. To adjust the stripper platevertically, provision is made of compactly nested threaded rings and, toorient the punch angularly, provision is made of an adjusting mechanismwhich acts on a rod projecting from the upper end of a hydrauliccylinder and connected to a downwardly projecting ram for reciprocatingthe punch.

10 Claims, 8 Drawing Figures 1 PUNCH PRESSWITH SAFETY noon BACKGROUND OFTHE INVENTION This invention relatesto a punch press with a reciprocablepunch which coacts with an underlying die to punch holes in anintervening workpiece. More particularly, the invention relates to apunch press of the type in which the punch is carried on the end of aram anchored to a piston which is adapted to be reciprocated back andforth within a cylinder in response to the admission of pressure fluidalternately into opposite ends of the cylinder.

A punch press of the same general type as the present press is disclosedin Scott, U.S. Pat. No. 3,720,125. In such a press, the punchreciprocates through a stripper plate which strips the workpiece fromthe punch as the latter is retracted out of the newly formed hole. Thestripper plate is adjustable toward and away from the die to accommodateworkpieces of different thicknesses and is carried on the end of atubular housing which extends alongside and generally encloses thepunch.

SUMMARY OF THE INVENTION One of the aims of the present invention is toprovide a punch press with a new and improved stripper housing whichcompletely surrounds the punch and pre vents the press operator fromgaining access to the punch unless the press is disabled in such amanner as to make it safe for the operator to insert his hands into thehousing and between the punch and the stripper plate.

A more detailed object is to achieve the foregoing through the provisionof a stripper housing having an access door which is latched closedduring the normal punching cycle of the press and which cannot be openeduntil the punching cycle has been terminated and the punch has beenmoved to a fully retracted position.

A further object is to provide a comparatively simple latch whichreciprocates with the punch and latches the door closed during thenormal punching cycle and then automatically unlatches the door when thecycle is completed and the punch is held in a safely retracted position.The invention also resides in the provision of a manually releasabledetent which holds the door closed until the latter becomes held by thelatch at the start of the punching cycle.

Still another object is to provide relatively simple means forpreventing operation of the press unless the door is closed and forautomatically and immediately stopping the punching cycle in the eventthe door should be forced open during such cycle.

These and other objects and advantages of the invention will become moreapparent from the following detailed description when taken inconjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a fragmentary frontelevation of a new and improved punch press embodying the novel featuresof the present invention, parts of the press being broken away and shownin section and the hinged door being shown in an open position.

FIG. 2 is a fragmentary cross-section taken substantially along the line22 of FIG. 1 and showing the hinged door in a closed position.

FIG. 2A is an enlarged view of parts shown in FIG. 2.

FIG. 3 is a fragmentary view similar to FIG. 2 but showing parts inmoved positions.

FIG. 4 is a radialcross-section taken through the stripper housing anddiagrammatically showing a pneumatic circuit which is associated withthe door.

FIG. 5 is-a fragmentary perspective view of the housing and the door,the latter being shown in an open position.

FIG. 6 is a fragmentary top plan view of the press as taken along theline 66 of FIG. 2.

FIG. 7 is an exploded perspective view of parts shown in FIG. 6.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT The specific presswhich has been illustrated is numerically controlled and is particularlysuitable for performing high speed nibbling operations in which thepunch nibbles away successive portions of the workpiece to form acontoured hole or to shape the edge of the workpiece.

In this instance, the punch 11 is carried in a suitable punch holder 15attached to the lower end of a vertically reciprocable rod or ram 16which forms part of a hydraulic actuator 17 having an uprightcylinder 19anchored to a horizontal support or mounting plate 20, the latter beingrigid with the bed 14 and overhanging the die 13. The upper end of theram 16 is connected to the lower end of a piston 21 which isreciprocated upwardly and downwardly in response to pressure fluid beingalternately admitted-into and dumped from opposite ends of the cylinderunder the control of a suitable valve (not shown).

Overlying the die 13 and disposed just above the workpiece I5 is acircular stripper plate 23 formed with a central hole 24 through whichthe punch 11 reciprocates during a normal punching cycle. As the punchis retracted through its upstroke, the stationary stripper plate engagesthe workpiece and thus strips the workpiece from the punch.

In a typical numerically controlled cycle, the punch 11 isreciprocatedthrough several successive working strokes and moves betweenadvanced and retracted positions during each stroke. Thus, the punchadvances sufficiently far into the die 13 to nibble off a portion of theworkpiece 15 and then is retracted upwardly to the position shown inFIG. 3 in which the extreme lower end of the punch is disposed withinthe opening 24 in the'stripper plate 23. After the workpiece has beenrepositioned, the punch is again advanced downwardly through thestripper plate and into the workpiece. Upon the completion of a givennibbling operation, it may be necessary to replace the punch, the dieand the stripper plate with tooling of a different size or shape beforeproceeding to perform the next operation. When the tooling is to bechanged at the end of an operation, the numerical control automaticallyterminates the normal working stroke at the proper time and causes theram 16 to retractthe punch upwardly beyond its normal retracted position(FIG. 3) and to stop the punch in an upper tool change position shown inFIGS; 1 and 2. When raised to the latter position, the punch mayberemoved easily from the punch holder by the press operator and the ram16 cannot be reciprocated inan automatic cycle until the operatormanually re-starts the numerical control.

In accordance with an important aspect of the present invention, thestripper plate 23 is mounted on the lower end of a tubular housing 27which completely encloses the punch 1 1 and the ram 16 and whichincludes an access door 29 that cannot be opened until the punch isretracted to its upper tool change position and y it is safe for thepress operator to place his hands in the housing. As long as the punchis being reciprocated through its normal working stroke or is stoppedout of its tool change position, the door is latched closed and cannotbe opened either intentionally or inadvertently by the operator. Whenthe punch is retracted to its tool change position, the door isautomatically unlatched and may be opened for purposes of changing thepunch and the stripper plate 23. Accordingly, the housing 27 of thepresent invention protects the operator from injury and yet enables theoperator to gain easy access to the punch when safe conditions prevail.

4 More particularly, the tubular'housing 27 is of circular cross-sectionand is connected at its upper end to the lower end of the cylinder 19 ina manner to be described subsequently. in addition to the door section29, the housing includes a fixed section defined by an upper cylinder 30(see FIG. 5) and by a lower half cylinder 31 located directly beneaththe cylinder and opening toward the front of the press 10. The door 29also is shaped as a half cylinder and is hinged to one edge portion ofthe half cylinder 31. When the door is closed, its free edge mates withand engages the opposite edge of the half cylinder 31 and the housingthus defines a complete cylinder from its top to its bottom.

The stripper plate 23 projects just below the lower edge of the housing27 and is formed on its upper side with a radially extending flange 33(FIG. 5) which fits snugly but releasably. into a complementary groove34 formedaround the inner side of the door 29 and the half cylinder 31.When opened, the door pulls away from the stripper plate and the latterthen may be removed easily from the housing 27 simply by pulling theplateradially out of the'half cylinder 31. To mount the door 29 forhinging on the half cylinder 31, a large car 36 (FIG. 5) is formed alongone edge portion of the half cylinder and fits between a pair ofvertically spaced smaller ears 37 formed on the adjacent edge portion ofthe door. A vertical hinge pin 38 (FIG. 4) extends {through holes in theears and is threaded at its upper end into the lower edge of thecylinder30. The door thus swings about the pin in moving between its open andclosed positions. To facilitate opening and closing of the door, ahandle 39 is secured to the edge portion of the door opposite the hinge.

in carrying out the invention, a latch 40 (FIGS. 2 and 3) reciprocateswith the punch 11 and coacts with a strike 41 on the inner side of thedoor 29 to latch the latter closed unless the punch is in its toolchange position shown in FIG. 2. Herein, the latch comprises anelongated finger secured to one side of the punch holder 15 by screws 43and projecting downwardly alongside the punch holder, the finger beingspaced radially outwardly from the holder with its lower end located inthe same plane as the lower surface of the holder. The strike 41 islocated near the upper end of the door and midway between the side edgesthereof and comprises a block 44 (FIG. 4) fastened to the door by screws45 and formed with an upwardly opening hole 46 for slidably receivingthe latch finger 40.

When the punch 11 is retracted upwardly to its tool change position, thelatch finger 40 is spaced above the strike 41 as shown in FIG. 2 andthus the door 29 can be swung open about the hinge pin 38 to enable theoperator to gain access to the punch and the stripper plate 23. When thedoor is closed and the punch is advanced downwardly from its tool changeposition, the latch finger 40 telescopes into the hole 46 in the strikeand prevents the door from being opened. The latch finger remainstelescoped with the strike even when the punch is shifted upwardly toits normally retracted position (see FIG. 3) during the working strokeand thus the operator cannot open the door while the punch isreciprocating or when the punch is in any position other than its toolchange position. Accordingly, the danger of the operator being injuredis substantially reduced since all of the reciprocating elements abovethe stripper plate 23 are enclosed and since access to the housing 27cannot be gained until the punch is retracted to its tool changeposition to pull the latch finger 40 out of the strike 41.

Advantageously, provision is made of a releasable detent 50 (FIGS. 2 and2A) for holding the door 29in its closed position after the door hasbeen shut and before the punch 11 is shifted downwardly to advance thelatch finger 40 into latching engagement with the strike 41. In thisinstance, the detent comprises a vertical plunger 51 (FIG. 2A) which isfitted slidably into a chamber 53 formed ina screw 54 which is threadedinto an upwardly opening hole 55 drilled in the upper edge of the doorjust outboard of the strike. A coil spring 56 is telescoped into thechamber 53 and urges the plunger 51 upwardly to a position in which theupper end of the plunger projects above the upper edge of the door. Whenthe latter is in its closed position, the plunger seats releasably in adownwardly tapered hole 56 drilled in the lower edge of the cylinder 30and serves to hold the door closed. After the latch finger 40 has beenreleased and as the door is pulled opened by the operator, the plungeris automatically cammed out of the hole 56 and, when the doorisre-closed, the plunger snaps into the hole to hold the door until thelatch 40 subsequently telescopes into the strike 41.

The invention also contemplates means forpreventing automatic cycling ofthe punch 11 if the door 29 is not closed and also for causing the punchto stop immediately if the door should happen to swing open during apunching cycle. Herein, these means comprise a sensing system 60 (FIG.4.) for detecting if the door is open or closed and operable when thedoor is open to produce an electrical signal for disabling automaticcycling of the punch.

Specifically, the sensing system 60 includes an air conduit 61 (FIGS. 4and 5) extending into the side of the half-cylinder 31 and communicatingwith a drilled passage 63 which opens out of the free side edge of thehalf-cylinder 31. When the door is closed, the end of the passage isblocked and sealed by a rubber pad 64 located in a hole drilled in thecorresponding side edge of the door 29.

During the time the door 29 is closed, the passage 63 is pressurized toa predetermined pressure with air introduced into the conduit 61 from acompressed air source 65 (FIG. 4), the air flowing through a pressureregulator 66 and an adjustable needle valve 67 before flowing into thepassage. As long as the passage is blocked by the closed door 29, thereis virtually no flow of air through the needle valve and thus there islittle if any pressure drop across the valve. When the door is opened,however, the air escapes rapidly from the portion of the conduit 61downstream of the needle valve and causes a much faster flow of airthrough the needle valve from the upstream portion of the conduit so asto create a larger pressure drop across the valve. A differentialpressure switch 69 is connected in parallel with the needle valve andtriggers from the position shown in full in FIG. 4 to the position shownin phantom when the differential pressure across the valve increases toa predetermined level as a result of the increased flow of air throughthe conduit. Upon triggering, the switch deenergizes a relay 70 which isconnected into the control circuit of the press and which is effectivewhen deenergized to prevent automatic cycling of the punch 1 1 from itstool change position. If the relay is deenergized while the press is ina working cycle, the punch is automatically stopped and the press isshut down.

Accordingly, the relay 70 is de-energized whenever the door 29 is openand thus prevents automatic cycling of the punch 11 until the door isclosed to aline the strike 41 with the latch finger 40. Should thestrike break or pull loose from the door during the punching operation,the punch 11 will be immediately stopped if the door flies open andcauses de-energization of the relay.

In addition to guarding the safety of the press operator, the latch 40and the sensing system 60 help prevent damage to the press 10. In mostinstances, the sheet metal workpiece 14 is bowed or buckled to someextent and, upon being re-positioned beneath the punch 11, pushesupwardly and laterally against the stripper plate 23 and tends to forcethe door 29 open. The latch keeps the door tightly closed and thus holdsthe stripper plate in its proper position so that the plate will not beshifted laterally and struck by the punch when the latter is advanceddownwardly. If the latch or the strike 41 should fail and the doorforced open during repositioning of the workpiece, the sensing system 60will stop automatic cycling of the machine and prevent downward shiftingof the punch. Thus, there is little danger of the punch striking andjamming against the stripper plate 23.

Extremely vertically compact mechanism 70 (FIG. 1) is provided beneaththe cylinder mounting plate 20 for adjusting the stripper housing 27upwardly and downwardly so as to enable vertical adjustment of thestripper plate 23 to accommodate workpieces of different thicknessesbetween the stripper plate and the die 13. As shown in FIG. 1, theadjusting mechanism 70 comprises an inner ring 71 which is telescopedover the lower end portion of a cylindrical, sleeve-like nose 73 formedintegrally with and depending from the cylinder 19. The nose projectsdownwardly through a hole 74 in the cylinder mounting plate 20 andslidably receives the ram 16 to help guide and rigidly support thelatter during reciprocation of the punch 11.

The inner ring 71 is internally threaded with threads of one hand and isexternally threaded with threads of equal pitch but of the oppositehand, the ring being threaded onto the cylinder nose 73 so as to move upwardly and downwardly on the nose when rotated. Rotation of the ring inthis particular instance is effected by a reversible rotary fluid motor75 (FIG. 1) which is advantageously supported above the cylindermounting plate 20 and whose drive shaft 76 carries a pinion 77positioned to mesh with a second pinion 79 on the upper end of anupright shaft 80 projecting downwardly through the cylinder mountingplate 20. A gear 81 is fastened to the shaft 80 immediately below thecylinder mounting plate and meshes with gear teeth 83 formed around theouter periphery of the ring 71 just above the external threads thereon.Thus, when the motor 75 is energized, the shaft 80 is rotated to turnthe ring 71 and cause the latter to thread upwardly and downwardly onthe cylinder nose 73.

Threaded onto the external threads of the inner ring 71 is anon-rotatable outer ring 85 (FIG. 1) which is connected to the stripperhousing 27 by means of angularly spaced shear pins 86 (FIG. 1) extendingradially between the stripper housing and the outer ring. If the punch11 should happen to strike the stripper plate 23 during the downstrokeof the punch, the shear pins 86 will fracture to allow the housing 27 topull loose from the outer ring 85 and, as a result, the ram 16 cancomplete its downstroke and the housing 27 will not be damaged by thepunch jamming against the stripper plate.

To prevent rotation of the stripper housing 27 and the outer ring 85, aradially projecting bracket 87 is attached rigidly to the outer ring andis formed with a hole 88 which slidably and rotatably receives the lowerend portion of the shaft 80. Thus, the shaft is free to rotate withinthe bracket but prevents turning of the outer ring 85 and permits thelatter to move upwardly and downwardly.

With the foregoing arrangement, lowering of the stripper plate 23 iseffected by driving the motor 75 in one direction so as to turn theinner ring 71 and cause the latter to thread downwardly on the cylindernose 73. The outer ring 85 and the stripper housing 27 are carrieddownwardly with the inner ring and, being held against rotation, theouter ring also threads downwardly on the inner ring. Accordingly, thestripper housing 27 and the stripper plate 23 are shifted downwardlythrough a distance which is twice as great as the downward displacementof the inner ring 71. Upward adjustment of the stripper plate is carriedout in a similar manner by driving the motor in the opposite directionto cause the rings to thread upwardly.

As a result of thetwo threaded rings 71 and 85, the stripper plate 23may be lowered through small increments and over a relatively wide rangeby moving the inner ring only a short distance downwardly from thecylinder-mounting plate 20. Because the outer ring 85 is threaded ontothe inner ring 71, the two rings are nested radially not only with oneanother but also with the cylinder nose 73 and thus the adjustingmechanism 70 is very compact in a vertical direction. Such compactnessenables a reduction in the vertical distance between the die 13 and thebottom of the cylinder mounting plate 20 to permit the use of acomparatively short ram 16. The short ram thus is less likely to deflectlaterally under the lateral forces exerted on the ram as the punch 11impacts against the workpiece 15 during the nibbling operation and, inaddition, lateral forces of smaller magnitude are transmitted back tothe cylinder 19 by the ram. Accordingly, the ram itself is comparativelyrigid and remains rigidly supported in the cylinder.

The rigidity of the lateral support of the ram 16 is increased stillfurther by means of an upwardly projecting rod 90 (FIGS. 1 and 7) whichis integral'with the upper end of the piston 21. As shown in FIG. 1, therod 90 extends upwardly out of the upper end of the cylinder 19 and isguided for up and down sliding by a cap 91 connected to the cylinder andclosing off the upper end thereof. By'virtue of the rod being guidedwithin the cap 91, additional radial support is provided to counteractthe lateral forces imposed on the ram 16 during the nibbling operationand to resist cocking of the ram and the piston 21 in the cylinder 19.

The ram 16 is oriented and locked in a precisely predeterminedangularposition in the cylinder 19 by rugged and comparatively,trouble-free mechanism 95 (FIGS. 2, 6 and 7) which acts on the upwardlyprojecting rod 90 to orient and lock the ram. Orientation of the ram inthe cylinder enables proper angular orientation of the punch l l and,with the orienting and locking mechansim 95 acting on the rod 90 andbeing located above the cylinder mounting plate 20, the area below theplate isunencumbered by the mechanism to help maintain a comparativelyshort vertical dimension between the plate andthe die 13 so that a shortram may be used.

In this instance, the orienting and locking mechanism 95 comprises acup-shaped collar 96 (see FIG. 7) which is telescoped onto the upper endportion of the rod. 90 and is anchored thereto by angularly spacedscrews 97. A depending pin 99 is rigid with the collar and fits tightlyintoa keyway 100 in the upper end of the rod to locate the collar in aprecise angular position on the rod.

Telescoped over the lower end portion of thecollar 96 is a ring 101(FIG. 7) which is fastened to the collar by radially extending pins 103and is held in an accurately established angular-position on the collarby a square key 104 fittedinto a keyway 105 in the side of the collar. Asplit ring 106 is telescoped over the upper end portion of the collar 96immediately above the lower ring 101 and is adapted to be clampedsecurely to the collar by a bolt 107. When the bolt is loosened, thecollar 96 may be turned within the split ring 106 to enable angularorientation of the rod 90 and the ram 16. v

As shown in FIGS. 2 and 7, the lower ring 101 is formed with a radiallyprojecting arm 110 which is disposed immediately below an arm 111projecting radially from and formed integrally with the split ring 106.

The arm 111 is held in an angularly fixed postion and, when the splitring 106 is unclamped from the collar 96, the arm 110 may be adjustedangularly relative to the fixed arm 11!. To enable adjustment of the arm1 10, an upright dowel l 13 is press-fitted into a hole 1 14 (FIG. 2) inthe arm 110 and projects upwardly into an enlarged hole 115 formed inthe arm 111. Two adjusting screws 116 are threaded into radiallyextending holes 117 in the arm 111 and are positioned with their freeends or tips in engagement with the dowel 113.

When the split ring 106 is unclamped, one of the adjusting screws maybeloosened and the other tightened to shift the dowel 113 within thehole and thereby adjust the ring 101, the collar 96 and the rod 90angularly relatively to the angularly fixed split ring. In this way, theram 16 may be adjustably oriented in a proper angular positionwithin-the cylinder 19. After the ram has been oriented, both adjustingscrews 1 16 are tightened against the dowel 113 and are clamped in placeby lock nuts 119 located between the sides of the arm 1 1 l and theheads of the screws. The split ring 106 then is tightened by means ofthe bolt 107 and clamps securely against the collar 96 to preventturning of the rod 90 and the ram 16.

To hold the arm 106 in an angularly fixed position, a hardened post 120(FIGS. 6 and 7) of square crosssection is anchored to a plate 121connected to and extending outwardly from the cylinder cap 91. The postprojects upwardly from the plate, is disposed alongside the outer end ofthe arm 106 and coacts with two antifriction rollers 123 and 124 toguide the arm for up and down reciprocation with the rod 90 whilepreventing turning of the arm. As shown in FIG. 6, the anti-frictionrollers are journaled on the free outer end of the arm 106 and arelocated on opposite sides of the post 120 to ride up and down on thelatter when the arm is moved upwardly and downwardly as the rod 90 isreciprocated. The rollers fit snugly against the sides of the post andthus prevent the arm 106 from turning angularly relative to the post.

With the foregoing arrangement, the rollers 123 and 124 establish arolling connection between the arm 106 and the post 120 to avoid theuseof a sliding guide con nection for the arm and hence virtually eliminatethe creation of heat at the connection was the rod 90 is reciprocated atrapid rates ranging upwardly to 600 strokes per minute. Because the arm106 remains angularly stationary when the rod 90 is adjusted by thescrews 116, the rollers always remain in face-to-face contact with thesides of the square post 120 and thus always roll smoothly along thepost without cocking or binding and without being subjected to excessivewear as otherwise would occur in the case of line contact between therollers and the post. The two adjusting screws 116 are capable ofshifting the rod 90 angularly through small, precise increments and thusthe angular position of the rod may be accurately established to insureproper angular orientation of the punch 11.

As mentioned above, encumbrance between the die 13 and the cylindermounting plate 20 is reduced by locating the orienting and lockingmechanism 95 above the mounting plate and by arranging the mechanism toact on the upwardly projecting rod 90. Such encumbrance is reduced stillfurther using the rod to actuate means'for signaling the verticalposition of the punch 11. Herein, these means comprise two proximityswitches and 131 (FIGS. 6 and 7) supported in vertically andhorizontally spaced relation on a bracket 133 upstanding from the plate121. A second bracket 134 is anchored to and projects outwardly from thearm 106 and carries a pair of horizontally spaced lugs 135 and 136 whichmove upwardly and downwardly past the switches as the punch 11 isreciprocated. When a tool changing operation is to be performed, the lug135 triggers the switch 130 when the punch has been shifted upwardly toits tool changing position, and the switch produces an electrical signalto stop the ram 16 with the punch in that position. When the punch hasshifted downwardly into the die 13 a predetermined distance during thenormal working stroke of the punch, the lug 136 triggers the switch 131to produce a signal causing the ram to reverse directions and shift thepunch upwardly.

To effect reversal of the ram 16 when the punch 11 is shifted upwardlyto its normally retracted position (FIG. 3), a proximity switch 140 issupported on the upper cylinder 30 of the stripper housing 27 and isadapted to be triggered by a lug 141 which is carried on the punchholder 15. While the proximity switch 140 is carried on and adjustablevertically with the stripper housing 27 for the advantageous purposedisclosed in the aforementioned application, the switches 130 and 131 ofthe present punch press are removed from the housing and are locatedabove the cylinder mounting plate 20 so that the area below the plate isnot encumbered by such switches.

We claim:

1. A punch press having a support, a vertically reciprocable ram on saidsupport and normally operable to shift a punch downwardly and upwardlythrough a working stroke between retracted and advanced positions, saidram being selectively operable to shift the punch upwardly beyond saidretracted position to a tool change position, a tubular housing mountedon said support and surrounding said punch, a stripper plate supportedon the lower end of said housing and formed with a hole within whichsaid punch reciprocates during said working stroke, said housingcomprising a fixed section and a door section hinged on said fixedsection to swing outwardly and inwardly relative to the latter about anupright axis between closed and open positions, a strike mounted on saiddoor section, and a latch movable with said ram and engageable with saidstrike during said working stroke to hold said door section in saidclosed position but automatically releasable from the strike to permitoutward swinging of said door section to said open position when saidram shifts said punch upwardly to said tool change position.

2. A punch press as defined in claim 1 in which said latch comprises adownwardly projecting finger movable with said ram, said strikecomprising a member secured to the inner side of said door section andformed with an upwardly opening hole for slidably receiving said finger.

3. A punch press as defined in claim 1 further including means operableindependently of said latch for holding said door section in said closedposition and selectively releasable to permit swinging of said doorsection to said open position when said punch is in said tool changeposition.

4. A punch press as defined in claim 3 in which said means comprise adetent mounted on one of said sections and movable into latchingengagement with the other section automatically as an incident toswinging of said door section to said closed position.

5. A punch press as defined in claim 4 in which said detent comprises aplunger mounted for endwise movement in said one section, a springbiasing said plunger toward the other section, and a hole in said othersection for receiving said plunger when said door section is in saidclosed position and shaped to automatically release said plunger as saiddoor section is swung toward said open position.

6. A punch press as defined in claim 1 further including meansresponsive to the position of said door section and operable to producea signal when the door section is out of said closed position, and meansresponsive to said signal for preventing movement of said ram throughsaid working stroke.

7. A punch press as defined in claim 6 further including a passageway inone of said sections and having an open end which is blocked by theother of said sections when said door section is in said closed positionand which is unblocked when said door section is in said open position,means for introducing pressurized air into said passageway and operableto pressurize the latter to a preselected pressure level when said doorsection is in said closed position, and said signal producing meansbeing operable to produce an electrical signal in response to thepressure in the passageway dropping below said level when said doorsection is moved to said open position and the end of the passageway isunblocked.

8. A punch press comprising a support, a reciprocable ram on saidsupport and normally operable to shift a punch through a working strokebetween and retracted and advanced positions, said ram being selectivelyoperable to retract the punch beyond said retracted position to a toolchange position, a tubular housing mounted on said support andsurrounding said punch, said housing comprising a fixed section and adoor section movable between open and closed positions relative to saidfixed section, and means for preventing movement of said door sectionfrom said'closed position at all times during said working stroke andoperable to permit movement of said door section to. said open positionwhen said ram retracts said punch to said tool change position.

9. A punch press as defined in claim 8 in which said means comprises alatch reciprocable with said ram, and a strike on the inner side of saiddoor section and telescoping with said latch during said working stroke.

10. A punch press comprising a support,'a reciprocable ram on saidsupport and normally operable in an automatic cycle to shift a punchthrough a working stroke between retracted and advanced positions, atubular housing mounted on said support and surrounding said punch, saidhousing comprising a fixed section and a door section movable betweenopen and closed positions relative to said fixed section, means forreleasably holding said door section in said closed position, apassageway in one of said sections and having an open end which isblocked by the other of said sections when said door section is in saidclosed position and which is unblocked when said door section is in saidopen position, means for introducing pressurized air into saidpassagewayand operable to pressurize the lat ter to a preselected pressure levelwhen said door section is in said closed position, signal producingmeans operable to produce an electrical signal in response to thepressure in the passageway dropping below said level when said doorsection is moved to said open position and the end of the passageway isunblocked, and means responsive to said signal for preventing automaticcycling of said ram through said working stroke. a

1. A punch press having a support, a vertically reciprocable ram on saidsupport and normally operable to shift a punch downwardly and upwardlythrough a working stroke between retracted and advanced positions, saidram being selectively operable to shift the punch upwardly beyond saidretracted position to a tool change position, a tubular housing mountedon said support and surrounding said punch, a stripper plate supportedon the lower end of said housing and formed with a hole within whichsaid punch reciprocates during said working stroke, said housingcomprising a fixed section and a door section hinged on said fixedsection to swing outwardly and inwardly relative to the latter about anupright axis between closed and open positions, a strike mounted on saiddoor section, and a latch movable with said ram and engageable with saidstrike during said working stroke to hold said door section in saidclosed position but automatically releasable from the strike to permitoutward swinging of said door section to said open position when saidram shifts said punch upwardly to said tool change position.
 2. A punchpress as defined in claim 1 in which said latch comprises a downwardlyprojecting finger movable with said ram, said strike comprising a membersecured to the inner side of said door section and formed with anupwardly opening hole for slidably receiving said finger.
 3. A punchpress as defined in claim 1 further including means operableindependently of said latch for holding said door section in said closedposition and selectively releasable to permit swinging of said doorsection to said open position when said punch is in said tool changeposition.
 4. A punch press as defined in claim 3 in which said meanscomprise a detent mounted on one of said sections and movable intolatching engagement with the other section automatically as an incidentto swinging of said door section to said closed position.
 5. A punchpress as defined in claim 4 in which said detent comprises a plungermounted for endwise movement in said one section, a spring biasing saidplunger toward the other section, and a hole in said other section forreceiving said plunger when said door section is in said closed positionand shaped to automatically release said plunger as said door section isswung toward said open position.
 6. A punch press as defined in claim 1further including means responsive to the position of said door sectionand operable to produce a signal when the door section is out of saidclosed position, and means responsive to said signal for preventingmovement of said ram through said working stroke.
 7. A punch press asdefined in claim 6 furtHer including a passageway in one of saidsections and having an open end which is blocked by the other of saidsections when said door section is in said closed position and which isunblocked when said door section is in said open position, means forintroducing pressurized air into said passageway and operable topressurize the latter to a preselected pressure level when said doorsection is in said closed position, and said signal producing meansbeing operable to produce an electrical signal in response to thepressure in the passageway dropping below said level when said doorsection is moved to said open position and the end of the passageway isunblocked.
 8. A punch press comprising a support, a reciprocable ram onsaid support and normally operable to shift a punch through a workingstroke between and retracted and advanced positions, said ram beingselectively operable to retract the punch beyond said retracted positionto a tool change position, a tubular housing mounted on said support andsurrounding said punch, said housing comprising a fixed section and adoor section movable between open and closed positions relative to saidfixed section, and means for preventing movement of said door sectionfrom said closed position at all times during said working stroke andoperable to permit movement of said door section to said open positionwhen said ram retracts said punch to said tool change position.
 9. Apunch press as defined in claim 8 in which said means comprises a latchreciprocable with said ram, and a strike on the inner side of said doorsection and telescoping with said latch during said working stroke. 10.A punch press comprising a support, a reciprocable ram on said supportand normally operable in an automatic cycle to shift a punch through aworking stroke between retracted and advanced positions, a tubularhousing mounted on said support and surrounding said punch, said housingcomprising a fixed section and a door section movable between open andclosed positions relative to said fixed section, means for releasablyholding said door section in said closed position, a passageway in oneof said sections and having an open end which is blocked by the other ofsaid sections when said door section is in said closed position andwhich is unblocked when said door section is in said open position,means for introducing pressurized air into said passageway and operableto pressurize the latter to a preselected pressure level when said doorsection is in said closed position, signal producing means operable toproduce an electrical signal in response to the pressure in thepassageway dropping below said level when said door section is moved tosaid open position and the end of the passageway is unblocked, and meansresponsive to said signal for preventing automatic cycling of said ramthrough said working stroke.